Dynamics of the Hippocampus During Encoding and Retrieval of Face-Name Pairs

Science, 299(5606):577-580, January 24 2003.

Michael M. Zeineh^1,2, Stephen A. Engel³, Paul M. Thompson⁴, Susan Y. Bookheimer¹

¹Ahmanson-Lovelace Brain Mapping Center, 660 Charles E. Young Dr. South, University of California Los Angeles, Los Angeles, CA 90095-7085
²Interdepartmental Neuroscience Ph.D. Program, Medical Scientist Training Program, UCLA School of Medicine
³ UCLA Department of Psychology, Franz Hall, 1282a, Los Angeles, CA 90095-1563
⁴ Laboratory of Neuro Imaging, Department of Neurology, Division of Brain Mapping, UCLA School of Medicine, Los Angeles, CA 90095-1769

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ABSTRACT

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The medial temporal lobe (MTL) is critical in forming new memories. Using new high-resolution functional magnetic resonance imaging (fMRI) acquisition and analysis methods, we identified unique computational properties of different subregions within the hippocampal circuitry as human subjects committed new associations to memory. The CA fields and dentate gyrus were active only during encoding, and activity changed dynamically in proportion to the amount of new information undergoing successful encoding. In the subiculum the same temporal pattern was found, but only during recall. In contrast to the transient hippocampal activity during memory acquisition, left anterior prefrontal cortical activity was correlated with the total number of associations recalled and stored. Our results demonstrate that individual structures within the hippocampus are differentially involved in encoding and retrieval. As learning progresses, frontal cortex becomes more engaged and the role of the hippocampus in retrieval diminishes.

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